For miniaturization of devices, there has recently been widespread use of display devices each having a combination of a display section and an input section and a touch panel function. In particular, in portable terminals such as cellular phones, PDAs (personal digital assistants), and tablet PCs, there has been widespread use of display devices each including a touch panel that can detect a position of contact of a finger or a stylus with a surface on the display section.
Conventionally, there have been known various types of touch panel such as resistive (pressure-sensitive) touch panels and capacitive touch panels. Of these touch panels, capacitive touch panels have been widely used.
A capacitive touch panel detects a position of contact by detecting a change in capacitance as effected when a finger or a stylus touches the display screen. This makes it possible to detect a position of contact with a simple operation.
Further, unlike a resistive touch panel, a capacitive touch panel does not require the formation of two conducting films with an air layer sandwiched therebetween and therefore does not suffer from interfacial reflection of outside light by the interface between the air layer and either conducting film.
On the other hand, however, since a capacitive touch panel detects a position of contact by detecting a change in capacitance, exposure of the touch panel to noise causes a change in lines of electric force, thus posing a risk of making the touch panel unable to accurately detect a position of contact.
Conventionally widely-used examples of touch panels are out-cell touch panels or on-cell touch panels (for example, see Patent Literature 1) that are mounted on the outer side of a display panel.
In such a case of a touch panel provided on the outer side of a display panel, an overlap of the touch panel with the display panel undesirably causes increases in thickness and weight of the device as a whole.
Moreover, the mounting of the touch panel on the outer side of the display panel causes outside light to be reflected by the interface between the touch panel and the display panel, as well as on a surface of the touch panel, thus affecting contrast and viewability. Further, the mounting of the touch panel on the outer side of the display panel causes the touch panel per se to exhibit decreased viewability.
In view of these problems, in-cell touch panels each obtained by incorporating a touch panel into a cell in a display panel or the like have recently been under development from the point of view of a reduction in thickness, a reduction in weight, and an improvement in viewability, as well as cost advantages as such as a reduction in the number of components that is achieved by making the touch panel “in-cell” (for example, see Patent Literatures 2 and 3).
Patent Literatures 2 and 3 disclose a configuration in which a CF substrate is used as a touch panel substrate (i.e. an in-cell touch panel substrate) that constitutes an in-cell touch panel, with a sensor electrode built in between an insulating substrate in a CF substrate and a transparent counter electrode made of ITO (indium tin oxide), the sensor electrode serving as a position detection electrode that detects a position of contact of an object.
FIG. 10 is a set of diagrams (a) and (b) schematically showing a configuration of a liquid crystal display device 100 including a conventional in-cell touch panel substrate.
As shown in (a) of FIG. 10, the liquid crystal display device 100 includes a TFT (thin-film transistor) substrate 101, a CF (color filter) substrate 102, and a liquid crystal layer 103 sandwiched between the TFT substrate 101 and the CF substrate 102.
Moreover, the CF substrate 102, which is an in-cell touch panel substrate, includes: a transparent insulating substrate 104; a light-blocking layer 105 (which demarcates pixels, and overlaps the after-mentioned metal wire 108 when seen in planar view) formed in a predetermined shape on the transparent insulating substrate 104; sense electrodes 106a and drive electrodes 106b formed by transparent electrodes made of ITO or the like in the same plane as a sensor electrode serving as a position detection electrode to detect a position of contact of an object; an insulating layer 107 covering the sense electrodes 106a and the drive electrodes 106b; a metal wire 108 that causes sense electrodes 106a arranged in a straight line and electrically separated from each other to be electrically connected to each other via contact holes (not illustrated) formed in the insulating layer 107; an overcoat layer 109 including a different-colored color filter layer (not illustrated) covering the insulating layer 107 and the metal wire 108; and a transparent counter electrode 110 made of ITO or the like on the overcoat layer 109.
Meanwhile, although not illustrated, the TFT substrate 101 includes a plurality of TFT elements and a plurality of pixel electrodes connected to the TFT elements, respectively.
Moreover, as shown in (b) of FIG. 10, the metal wire 108 is needed because the sense electrodes 106a and the drive electrodes 106b, formed by transparent electrodes made of ITO or the like in the same plane as a sensor electrode serving as a position detection electrode to detect a position of contact of an object, are in the form of a single layer, and serves to make an electrical connection between sense electrodes 106 formed electrically separately from each other horizontally as shown in (b) of FIG. 10.